The Sense of Balance
Just as humans use their inner ear to stay upright and know which way is down, robots use IMUs. An IMU typically combines three types of sensors: an Accelerometer (gravity/force), a Gyroscope (rotation), and often a Magnetometer (heading).
Sensor Fusion
Raw data from these sensors is noisy or drifts. Fusion algorithms (like Kalman Filters) mathematically combine them to get a clean, stable orientation.
6-Axis vs 9-Axis
6-Axis: Accel + Gyro (Good for balance/drones, but yaw drifts).
9-Axis: Adds Compass (Fixes yaw drift, gives real North).